NAME
        Input -- Identify the program's initial input file handle

    SYNOPSIS
        file = Input()
        D0

        bptr input(void)

    FUNCTION
        Input() is used to identify the initial input stream allocated when
        the program was initiated.  Never close the filehandle returned by
        Input!

    RESULTS
        file - BCPL pointer to a file handle

    SEE ALSO
        output(), selectinput()